Due to a ban on plastic bags, many shoppers are swimming in reusable bags. Some retailers are embracing paper bags, but critics say they’re also bad for the environment.

What if a machine could suck up carbon dioxide from the atmosphere, run it through a series of chemical reactions, and essentially spit out industrially useful plastic?

At this point, most people know that microplastics are everywhere. Scientists have shown that tiny particles, amounting to ...